This application claims priority to Korean Patent Application No. 10-2004-0039627, filed on Jun. 1, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an information recording and/or reproducing apparatus, and more particularly, to an integrated optical system and a method of manufacturing the same, and an information recording and/or reproducing apparatus employing the integrated optical system.
2. Description of the Related Art
In an optical recording and/or reproducing apparatus that records arbitrary information on an optical information storage medium and reproduces information recorded on the optical information storage medium by focusing laser light using an objective lens, the recording capacity is determined according to the size of a focused light spot. The size (S) of a focused light spot is determined according to the wavelength (λ) of laser light and the numerical aperture (NA) of an objective lens is expressed below by Equation (1).S∝λ/NA  Equation (1)
Therefore, in order to reduce the size of a light spot focused on an optical information storage medium for a higher recording density, research into an optical recording and/or reproducing apparatus using a short wavelength light source such as a blue laser and an objective lens having an NA of 0.6 or greater has been conducted.
Since the development of compact discs (CDs) that require light with a wavelength of 780 nm and an objective lens having an NA of 0.45 or 0.5 to record information thereon and/or reproduce information therefrom, intensive research has been conducted into increasing the recording density and information storage capacity of the media. Digital versatile discs (DVDs), to/from which information can be recorded and reproduced using light having a wavelength of 650 nm and an objective lens having an NA or 0.6 or 0.65, were obtained as a result of the research.
Recently, there has been steady progress in research into high-density information storage media using blue light having a wavelength of, for example, 405 nm, and having a recording capacity of 20 GB or greater.
There have been efforts to standardize high-density optical information storage media using blue light having a wavelength of, for example, 405 nm, and standards are being defined. A NA of an objective lens for a high-density optical information storage medium is 0.65 or 0.85, which will be described later.
The thickness of a DVD is reduced to 0.6 mm from 1.2 mm of a CD to provide adequate tolerance for tilting of the optical information storage medium because the NA of an objective lens is increased to 0.6 for the DVD from 0.45 for the CD.
In a high-density optical information storage medium having a higher storage capacity than a DVD, when the NA of an objective lens is increased to, for example, 0.85, the thickness of the high-density optical information storage medium must be reduced to about 0.1 mm.
A high-density optical information storage medium that has a reduced thickness and requires a greater NA objective lens is referred to as a Blu-ray Disc (BD). According to the standard for BDs, the wavelength of a light source is 405 nm, and the NA of an objective lens is 0.85. The standard thickness of BDs is about 0.1 mm.
In addition to BDs, (high definition) HD DVDs are currently under development as high-density optical information storage media. HD DVDs have the same substrate thickness and require an objective lens having the same NA as DVDs. Only the wavelength of a standard light source, that is, a blue wavelength of, for example, 405 nm, matches the standard for BDs.
In addition to the requirement for high-density, high-capacity optical information storage media, there is a need for a slimmer, smaller optical system constituting an optical pickup.
Along with the increasing need for the adoption of optical recording and/or reproducing apparatuses in portable terminals, such as personal digital assistants (PDAs), mobile phones, digital cameras, portable disc players, camcoders, etc., there has been an increasing need for slim optical pickups. For use in the field of portable terminals, optical pickups should be slim and small and be able to record and/or reproduce a large amount of information, such as music, moving pictures, etc., at high density.
However, there are technical limitations in manufacturing a small, slim optical system by reducing the sizes of optical elements constituting a conventional optical pickup that is currently used in optical recording and/or reproducing apparatuses for CDs and/or DVDs.
Furthermore, a conventional optical pickup is constructed by optically aligning and bonding a plurality of individually manufactured optical elements. Therefore, due to possible assembling errors in the assembling and aligning of parts, the reliability of the assembled optical pickup and the degree of automation are lowered.